Project Summary Over seven million Americans have an illicit substance use disorder (SUD)1, accruing annual costs of $11 billion in health care and $193 billion related to lost productivity and crime 2. Increasingly punitive approaches to SUD have been a costly and ineffective strategy to address this immense public health problem3-6. Incarceration costs $20,000 more per person per year than SUD treatment in the community7, and may increase substance use disorder and related risk behaviors, infectious disease, and mortality8-10. The punitive drug policy climate of recent decades has deepened racial disparities. Blacks account for one third of drug arrests, and 46% of persons convicted of drug felonies11. With a higher risk of arrests and prison sentences across the lifespan, Blacks are more vulnerable to criminal records that limit employment, housing, and education. These factors in turn are significant social determinants of health12. Research suggests that the disproportionate incarceration of Blacks contributes to Black-White disparities in mental and physical health13. Reducing criminal penalties through policy reform may be critical to improving health in minority populations. There is increasing recognition of the inadequacies of the criminal justice system to address substance use disorder. In 2014, California?s Proposition 47 (Prop 47) reduced criminal penalties for substance use by reclassifying all drug possession offenses to misdemeanors14, a model which other states are considering. Though the policy?s effects on arrests and jail populations are being investigated15, it is unknown how reducing penalties for drug possession has influenced substance use, treatment enrollment, and racial disparities in drug charges. This study will address these gaps. Investigating the health effects of social policy reforms such as Prop 47 will help to identify opportunities to improve health and health disparities on a population level. Aim 1 will assess whether reducing criminal penalties for drug possession altered the prevalence or severity of substance use, based on self-reports and illicit drug-related emergency department visits. Aim 2 will evaluate Prop 47?s impact on drug treatment enrollment overall and through the criminal justice system. Aim 3 will assess whether the policy reduced racial disparities in drug-related felonies. All analyses will use existing survey and administrative data, and methods developed to provide the strongest basis for causal inference in observational data settings, including difference-in-differences, instrumental variable analysis, regression discontinuity, and multi-level modeling of individual and county-level change. Criminal justice policy is in flux. This study is a timely opportunity to contribute to evidence-based policy reform to address health disparities. The proposed training, guided by a world-class mentorship team, will build the applicant?s expertise in methods for causal inference, theoretical frameworks for social determinants of health and substance use, and evidence-based policy processes. It will provide the necessary skills to study the macro-level determinants of health, including the criminal justice system, and policy solutions.